SELF-MONITORING OF BLOOD-PRESSURE AT HOME - HOW MANY MEASUREMENTS ARENEEDED

Objective To determine the minimum number of self-measurements of bloo d pressure at home (HBP) necessary to provide the maximum clinically i mportant benefit. Methods Hypertensive patients were randomly allocate d to monitor HBP for 2 weeks (6 work days, duplicate measurements, twi ce daily) or ambulatory blood pressure for 24 h. The alternative measu rement was then performed. Clinic blood pressure was measured at the b eginning and the end of the study. Criteria for reliability of HBP wer e the stabilization of mean HBP, its variability (SD) and the correlat ion coefficient r for relationship of HBP with ambulatory blood pressu re. The reproducibility of HBP was quantified using test-re-test corre lations and the SD of differences between average HBP values of differ ent days. Results We studied 189 patients (79 being administered stabl e antihypertensive treatment). Average HBP (137.5 +/- 16.2/85.9 +/- 9. 9 mmHg) was lower than average clinic blood pressure (P < 0.001) and h igher than 24 h and night-time ambulatory brood pressures (P < 0.001), There was no difference between HBP and daytime ambulatory blood pres sure. On day I HBP was higher than it was on each of days 2-6, with no difference among days 2-6. When data for the initial day for monitori ng of HBP were excluded from analysis, average HBP was reduced. Only a modest improvement in the reliability of HBP on day 2 (reductions in mean HBP and its SD and an increase in r with ambulatory blood pressur e) was achieved by averaging more readings taken on succeeding days. A t least two monitoring days were needed for the reproducibility of HBP to be superior to that of clinic blood pressure. Conclusions These re sults suggest that determining average HBP of the second and third wor k days, is the minimum programme that provides a reliable estimate of HBP. (C) 1998 Lippincott-Raven Publishers.